Decoherence induced spontaneous symmetry breaking - Quantum Physics

Abstract: We study time dependence of exchange symmetry properties of Bell states whentwo qubits interact with local baths having identical parameters. In case ofclassical noise, we consider a decoherence Hamiltonian which is invariant underswapping the first and second qubits. We find that as the system evolves intime, two of the three symmetric Bell states preserve their qubit exchangesymmetry with unit probability, whereas the symmetry of the remaining statesurvives with a maximum probability of 0.5 at the asymptotic limit. Next, weexamine the exchange symmetry properties of the same states under local,quantum mechanical noise which is modeled by two identical spin baths. Resultsturn out to be very similar to the classical case. We identify decoherence asthe main mechanism leading to breaking of qubit exchange symmetry.